1. Field of the Invention
The present invention relates to an image forming apparatus which develops highly fine images with liquid developer.
2. Description of Related Art
Heretofore, image forming apparatuses of a type that use liquid developer generally use the method of causing electrical migration of toner fine particles which are dispersed in an insulating liquid carrier such as aliphatic saturated hydrocarbon or the like, so that the toner fine particles adhere to the surface of a dielectric body on which an electostatic latent image is formed. This method enables the use of toner particles with smaller diameter than powder toner which is used in a developing device, and it is suitable for producing an image of a high resolution. This method is also advantageous that liquid toner needs less energy for fixing than powder toner. However, aliphatic saturated hydrocarbon used as liquid carrier generates a disagreeable smell. When the aliphatic saturated hydrocarbon is used, there is a concern for fires. Drying process is needed after images are formed by the aliphatic saturated hydrocarbon. Accordingly, the aliphatic saturated hydrocarbon is unsuitable for use in offices and homes.
Japanese Patent Publication No. 55-18906 has proposed another type of image developing device that uses liquid developer. According to the image developing device, a developer retainer is located in confrontation with and close to a latent image-forming body (photoconductive body). The surface of the latent image forming body is not immersed with liquid developer, but aqueous liquid developer is retained in the developer retainer. The developer retainer has a two-layered structure comprised from a hydrophilic layer and a water repellent layer. The water repellent layer presents a contact angle more than 90 degrees with respect to the liquid developer. The developer retainer is located such that the water repellent layer confronts the latent image-forming body. The developer retainer is formed with a number of fine through-holes. Each fine through-hole passes through both of the hydrophilic layer and the water repellent layer. The liquid developer is supplied into the fine through-holes from their open ends on the hydrophilic layer side. The liquid developer is retained in the fine through-holes because the liquid developer cannot enter the water-repellent portion due to the water-repellent property thereof. When an electrostatic latent image is formed on the latent image-forming body, the liquid developer is selectively attracted electrostatically toward the latent image-bearing body. As a result, the liquid developer advances or moves forward in the through-holes along their inner wall surfaces to enter the water-repellent portion. The liquid developer finally reaches the surface of the latent image-forming body, and adheres to the electrostatic latent image. Thus, the liquid developer develops the latent image into a visible image.
The above-described image developing device does not suffer from any disagreeable smell. The image developing device can be safely used without any fear of fires. The image developing device does not need drying processes after image formation.